1. Field of the Invention
The present invention relates to a fuel cell stack including a stack body formed by stacking electrolyte electrode assemblies and separators, and a box-shaped casing containing the stack body. Each of the electrolyte electrode assemblies includes a pair of electrodes and an electrolyte interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane (electrolyte) comprising a polymer ion exchange membrane. The electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly. The membrane electrode assembly is sandwiched between separators to form a fuel cell.
In use, normally, a predetermined number of (e.g., several tens to several hundreds of) fuel cells are stacked together to form a fuel cell stack to obtain a desired electrical energy. In the fuel cell stack, in order to prevent the increase of the internal resistance in the fuel cells, and degradation of performance due to leakage of reactant gases, it is necessary to reliably apply pressure to each of the stacked fuel cells and hold the stacked fuel cells.
In this regard, for example, a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2003-203670 is known. As shown in FIG. 8, the fuel cell includes a stack body 3 formed by stacking unit cells 2. Each of the unit cells 2 includes an electrolyte membrane and electrodes sandwiching the electrolyte membrane. End plates 4, 5 are provided at opposite ends of the stack body 3 in the stacking direction. Belleville springs 6 are provided between the end plate 5 and the stack body 3.
On each side surface of the stack body 3 along the stacking direction, a metal tension plate 7 is provided for applying a surface pressure to the stack body 3, and maintaining the surface pressure.
In particular, in the case where the fuel cell is mounted in a vehicle, a load from the outside tends to be applied to the fuel cells. In this case, when a compression load is applied to the fuel cell in the stacking direction of the unit cells 2, the tension plates 7 having low strength in comparison with the end plates 4, 5 tend to be deformed (buckled) easily. Thus, the tension plates 7 are deformed inwardly toward the stack body 3 or deformed outwardly in a direction away from the stack body 3. Therefore, the unit cells 2 and the harness and the other peripheral components outside the unit cells 2 may be damaged undesirably.